Global merge syntax can go through the child relationships and get data down there.   Here is an example: 

{{$Model.Account.data.0.Contacts.records.0.CreatedDate}}

Let me break that down: 

• Go to the Account model. 


• Get the first row of data


• Get the Contacts child relationship - and look for its records


• Get the first row of data from within the child relationship records


• Get the Created Date field…

Here what I am trying to accomplish. I would like to show in a reference field look up a UI_Field Long Text Area using the following. It looks like UI-field does not support "Long Text Area?